1. Field of the Invention
This invention relates to a synchronization signal detector for detecting synchronization signals (or frame synchronization signals) recorded on a recording medium, a method for detecting the synchronization signals, and a demodulator for demodulating data stored on a recording medium.
2. Description of the Related Art
For a disc recording system for a so-called compact disc (CD), as one of the disc-shaped recording media, such as an optical disc, magnetic disc or a magneto-optical disc, an eight-to-fourteen modulation (EFM) system is employed. With this modulation system, data are processed on the basis of 8 bits as a unit, and the 8-bit bit string is translated into a string of 14-channel bits.
The recording format for a CD is shown in FIG. 12 and in Table 1, in which 24 channel bit synchronization signals (frame synchronization signals), 14 channel bit sub-coding data, 336 (24.times.14) channel bit data and 112 (8.times.14) channel bit parity data are furnished. In addition, 3 bits each are furnished as margin bits for connecting the pattern data, thus totalling 102 channel bits. Meanwhile, as one of the roles of the margin bits, the maximum distance between transition of magnetization Tmax=11 T is adjusted for not being repeated twice for the synchronization signals. The encoding efficiency and the redundancy of the present recording format are 57.1% and 42.9%, respectively.
TABLE 1 ______________________________________ data channel bit ______________________________________ sync signals -- 24 subcoding 8 14 data 192 336 parity 64 112 margin bits -- 102 total 264 588 ______________________________________
The above-mentioned CD recording format is disadvantageous in that there is only one synchronization signal, margin bits are required for connecting the synchronization signals, and an exceptional bit string is set aside for the synchronization signals.
Meanwhile, each frame of the recording format for CD is composed of 588 channel bits, as shown above. If it is assumed that moving picture data is to be recorded on the CD-size disc, and the recording format is pursuant to the CD recording format and has a frame length longer than that provided in the CD recording format, the distance between the synchronization signals in the frame structure is increased, so that, if the frame structure synchronization is not in order, data restoration tends to be delayed.